The present invention generally relates to power boosters for vehicle brake systems and, more particularly, to an input push rod for applying an input force from a brake pedal to the power booster.
Brake power boosters generally utilize fluid pressure, or differentials thereof, to provide a power assist in applying force to the master cylinder of the brake system. Upon application of an input force on the brake pedal, an input member such as a push rod activates the power booster. The power booster intensifies the force applied to the input push rod by a calibrated amount and transfers the force to a power piston which then moves the master cylinder to apply the brakes at each wheel.
In the past, brake power boosters have incorporated electro-mechanical switches as part of the booster structure to cause illumination of the vehicle brake lights upon movement of the input rod. For example, power boosters have been designed that include an electrical circuit coupled to the brake illumination control system that causes illumination of the brake lights when the normally-open circuit is closed by a switch. The switch is typically biased in an open position and, in response to travel of the input push rod upon an input force being applied to the brake pedal, moves to a closed position to complete an electrical circuit that illuminates the brake lights. The brake illumination control circuit that includes a brake light driver circuit that causes illumination of the brake lights in response to closing of the electro-mechanical switch. The brake light driver circuit is typically separated or mounted remotely from the input push rod, and is electrically coupled to the electro-mechanical switch through an electrical cable.
Brake light control systems that use electromechanical switches to cause illumination of the vehicle brake lights have several drawbacks. For example, the brake booster and input push rod must be designed with additional structures for housing the switch arrangement and for attaching the switch actuation components to the input push rod. These additional structures increase the required space of the power booster which can give rise to installation difficulties when space is limited. Mounting of the brake illumination control system remotely from the input push rod and its associated electro-mechanical switch requires additional space and electrical connections within the vehicle.
Additionally, the electro-mechanical switch must be factory calibrated or adjusted to ensure that the brake lights are not illuminated when the input push rod is in a rest position, but are properly illuminated in response to a predetermined limited travel of the input push rod upon a force being applied to the brake pedal. Further, electro-mechanical switches used in brake light control systems may cause false illumination of the brake lights when the switch is jostled or the driver unintentionally causes travel of the input push rod in a non-braking situation.
For these general reasons, it would be desirable to provide a brake power booster system that accurately and reliably illuminates brake lights of a vehicle in response to a driver""s input on a brake pedal during a braking situation.
The present invention overcomes the foregoing and other shortcomings and drawbacks of brake systems heretofore known and, more particularly, of brake light control systems for causing illumination of brake lights. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with the principles of the present invention, an intelligent input push rod assembly is adapted to be operatively coupled at one end to a brake pedal and at an opposite end to a power booster of a brake system. The input push rod assembly is capable of applying a force to the power booster that is intensified and applied to a master cylinder of the brake system through a power piston and force output rod to apply the brakes at each wheel.
In accordance with one aspect of the present invention, the input push rod assembly includes a sensor that is capable of generating an electrical output having a magnitude that varies with the amount of force applied to the input push rod assembly by the brake pedal. The sensor generates an output voltage signal having a magnitude that is generally proportional to the input force applied to the input push rod assembly by the brake pedal. The output voltage signal generated by the sensor is applied to a brake light illumination system that is supported by the input push rod assembly. The brake light illumination system is operable to directly illuminate the brake lights of vehicle in response to the output voltage signal generated by the sensor. In this way, the input push rod assembly is an integral assembly that imparts an input force to the power booster to initiate a braking operation and includes the necessary brake light driver hardware to directly illuminate the brake lights.
The input push rod assembly includes a pair of elongated input push rod members and a housing member operatively connecting the pair of input push rod members so that the input push rod members extend generally along a common axis. The input push rods are biased for movement relative to each other by a spring and shunt assembly mounted within the housing member. In one embodiment of the present invention, the spring and shunt assembly comprises a pair of rigid shunt members that cooperate with a pair of respective Belleville springs to bias the input push rods for movement relative to each other along the common axis in response to an input force applied to the input push rod assembly. The shunt members are operable to limit compression or deflection of the Belleville springs through a generally linear force-deflection range of the springs so that the input push rods will move relative to each other only in the generally linear force-deflection operating range of the Belleville springs.
In accordance with another aspect of the present invention, the sensor comprises a rare earth magnet and a linear hall effect transducer that are mounted generally within the housing member. The magnet is mounted or affixed to one of the input push rods, and the linear hall effect transducer is mounted or affixed to a printed circuit board mounted to the housing member. The magnet and transducer are mounted offset from the common axis and in confronting relationship so that the magnet is mounted for reciprocal movement along a path parallel to and offset from the common axis, and the transducer is fixedly mounted adjacent the path of reciprocal movement. In response to movement of the input push rods relative to each other, the sensor is operable to generate the output voltage signal having a magnitude that varies with the amount of force applied to the input push rod assembly by the brake pedal.
The brake light illumination system coupled to the sensor includes a controller that executes an algorithm to perform two functions: (1) to calibrate a brake pedal rest position or brake pedal rest force so that the sensor is automatically compensated for temperature variations, vehicle pedal assembly mechanical tolerance differences and brake pedal assembly component wear; and (2) to determine whether a sufficient brake force has been applied to the input push rod assembly to cause direct illumination of the brake lights, thereby assuring that a predetermined force has been applied to the brake pedal before the brake lights are illuminated, and to turn the brake lights off at all other times.
The above features and advantages of the present invention will be better understood with reference to the accompanying figures and detailed description.